c# - 按钮命令不起作用，按钮位于 Collection View 内

Question

我在尝试通过单击按钮调用命令时遇到问题，这是我的代码，请帮忙后记，如果我将按钮从 collectionView 上移开，该命令就会起作用。命令的名称是 ButtonCommand ，我想我需要更多参数，帮助。

MaingPage.Xaml

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:d="http://xamarin.com/schemas/2014/forms/design"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         mc:Ignorable="d"
         x:Class="XamarinCollectionView.MainPage"
         xmlns:viewModels="clr-namespace:PruebaAppMap.ViewModels"
         xmlns:Models="clr-namespace:PruebaAppMap.Models"
         x:DataType="viewModels:MainPageViewModel"
         BackgroundColor="#2471A3">

<CollectionView  ItemsSource="{Binding Products}">
    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="Models:Product">
            <Frame
                Padding="5"
                CornerRadius="5"
                IsClippedToBounds="False">
                <Grid HeightRequest="100">
                    <Grid.ColumnDefinitions >
                        <ColumnDefinition Width=".3*"/>
                        <ColumnDefinition Width=".7*"/>
                        <ColumnDefinition Width=".4*"/>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height=".5*"/>
                        <RowDefinition Height=".5*"/>
                        <RowDefinition Height=".7*"/>
                    </Grid.RowDefinitions>
                    <Label Grid.Column="1" FontAttributes="Bold" FontSize="Large" VerticalOptions="Center" Text="{Binding Name}"/>
                    <Label Grid.Column="1" Grid.Row="1"  FontSize="Medium" Text="{Binding Price,StringFormat='{0:C}'}"/>
                    <Button Grid.Column="3" Grid.RowSpan="2" Grid.Row="1" x:DataType="viewModels:MainPageViewModel"  Text="Click me!" CommandParameter="{Binding}" Command="{Binding ButtonCommand}"/>
                </Grid>

            </Frame>

        </DataTemplate>
    </CollectionView.ItemTemplate>

</CollectionView>

View Model --MainPageViewModel

namespace PruebaAppMap.ViewModels{

public class MainPageViewModel
{

    public ObservableCollection<Product> Products { get; set; }
    public ICommand ButtonCommand { get; set; }
    public MainPageViewModel() 
    {
        Products = new ObservableCollection<Product>
        {
            new Product
            {
                Name="Yogurt",
                Price=5.50m,
                Image="yogurt.png",
                hasOffer=false

            },              

        };
        ButtonCommand = new Command(async () => await buton());
    }
    public async Task buton()
    {
        await App.Current.MainPage.DisplayAlert("Button pressed", "button was pressed", "ok");
    }}
}

Answer 1

正如 Jason 所说，DataTemplate 内按钮的 BindingContext 是 Product 的一个实例。未为产品定义 ButtonCommand。 ButtonCommand 在您的 ViewModel 中，因此您需要引用 ViewModel.ButtonCommand:

首先，为您的 ContentPage 命名，比如说 MyPage:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"

             x:Name="MyPage"

             x:Class="App266.MainPage">

在您的绑定(bind)中:

<Button Grid.Column="3" Grid.RowSpan="2" Grid.Row="1" Text="Click me!" Command="{Binding BindingContext.ButtonCommand, Source={x:Reference MyPage}}"/>

顺便说一句，不需要写x:DataType。

引用:Xamarin Button Command (inside of ListView.ItemTemplate) Not Firing